When designing room acoustics for audio production or reproduction, a key decision is the forms of treatment for the boundaries, whether absorptive or diffusive. Diffusion has been shown to be useful in treating a wide variety of spaces such as studios and concert halls. It is possible to design diffusers from rigid surfaces; any absorption in the room is then provided by separate elements. Alternatively, it is possible in one hybrid surface, not only to partially absorb the sound, but ensure that the reflected energy is diffused. Some commercial examples of such surfaces are available; they comprise a complex array of absorbent and reflective patches, referred to as Abffusor.RTM. or Diffsorbor.TM., Trademarks of RPG Diffusor Systems, Inc., with the former referring to devices that primarily absorb scattered energy and with the latter referring to devices that primarily diffuse scattered energy. Combined diffusive-absorptive surfaces may be formed through any one of a plurality of approaches, including covering an absorptive surface with a perforated reflective mask and combining reflective and absorptive elements. Examples of a mask are shown in FIG. 1A and 1B, where the rectangular or circular holes, respectively, (which may be almost any shape) provide absorption and the other areas provide complete reflection. The impedance changes across the surface provide diffusion. These new hybrid surfaces offer the designer an increased choice between the extremes of completely absorbing or diffusing, which may suit applications in performance spaces.
Co-Applicant D'Antonio is the patentee of U.S. Pat. No. 5,817,992, issued Oct. 6, 1998, for PLANAR BINARY AMPLITUDE DIFFUSOR. The D'Antonio patent discloses a flat faced panel having alternating reflective and absorptive regions or patches defined by a binary sequence consisting of zeros and ones with a flat power spectrum with the sequence being determined based upon shift register theory. In the D'Antonio patent, there are substantially equal numbers of reflective and absorptive regions or patches, respectively. The D'Antonio patent fails to contemplate optimization of the pattern of absorptive and reflective patches obtained through operation of a genetic algorithm. Furthermore, the present invention distinguishes from the D'Antonio patent as contemplating a pattern of absorptive and reflective patches or regions wherein the ratio therebetween may be other than 1:1, depending upon whether the resultant diffusor must have greater reflective or absorptive properties based upon the particulars of the intended location of installation.
In addition, the present invention distinguishes from the D'Antonio patent as contemplating a surface which may comprise a simple or compound curve rather than being planar, thereby offering a greater degree of diffusion. These curved combined diffusive-absorptive surfaces may be designed using 1-dimensional (1D) or 2-dimensional (2D) optimized binary element sequences with varying degrees of reflectivity.